/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshQueryFunctions.h
For the specified Triangle ID of the TargetMesh, get the Normal and Tangent vectors at each vertex of the Triangle. These Normals/Tangents will be taken from the Normal and Tangents Overlays, i.e. they will potentially be split-normals.
static [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * GetTriangleNormalTangents ( [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * TargetMesh, int32 TriangleID, bool & bTriHasValidElements, [FGeometryScriptTriangle](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptTriangle) & Normals, [FGeometryScriptTriangle](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptTriangle) & Tangents, [FGeometryScriptTriangle](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptTriangle) & BiTangents )